1. Field of the Invention
The present invention relates to a package and a package assembly, and more particularly, to a package and a package assembly for a power device.
2. Description of the Related Art
A power semiconductor device such as a silicon-controlled rectifier (SCR), a power transistor, an insulated-gate bipolar transistor (IGBT), a MOS transistor, a power rectifier, a power regulator, an inverter, a converter, or a combination thereof, is designed to operate at a voltage of 30V-1000V or greater. Since a power device operates at a high voltage, unlike a logic or memory device, its package must have excellent heat dissipation and high voltage insulation properties.
FIG. 1 is a sectional view of a conventional package 50 for a power device with a heat sink 60.
Referring to FIG. 1, a substrate 10 on which a power device 5 is formed is connected to a heat conductive electrical isolator 20 which, in turn, is connected to a metallic heat conductive plate 30 for heat release. The power device 5, the substrate 10, the isolator 20, and the conductive plate 30 are encapsulated by epoxy mold compound (EMC) or ceramic molding members. The encapsulated power device 5 is electrically connected to a lead 40 protruding outside the package 50.
In general, the metallic heat conductive plate 30 is exposed at the surface of the package 50. The heat sink (or a cooling block) 60 is connected to the exposed metallic heat conductive plate 30 to absorb and dissipate heat from the heat conductive plate 30. The heat sink 60 is generally formed of a metal having high heat conductivity. When the power device 5 operates at a high voltage, an electrical short may occur between the lead 40 of the package 50 and the heat sink 60. To prevent this, isolation distances such as a creepage distance L1 and a clearance distance L2 are determined considering the intended voltages such as the operation voltage and the impulse voltage when the package 50 and the heat sink 60 are designed. As the operation voltage and the impulse voltage of the power device increase, the creepage distance L1 and clearance distance L2 must also increase.
To increase heat dissipation capacity, it may be necessary to increase the area of the heat sink 60. For example, as illustrated in FIG. 1, the width of the heat sink 60 may increase from A1 to A2. To reduce the manufacturing cost of the heat sink 60 or for various other design considerations, the area of the heat sink 60 may also be increased. For example, one heat sink 60 may be used in the package for two power devices, to reduce the cost. Also, the contact area between the heat sink 60 and the package 50 may need to be increased to enhance heat transfer.
However, the width of the heat sink 60 may need to be restricted to maintain the clearance distance L2, and the contact area between the heat sink 60 and the package 50 may need to be restricted to maintain the creepage distance L1 in order to ensure isolation when the power device operates at a high voltage.